Generally, in a magnetic disk device, the magnetic head floats above the surface of the magnetic disk when it is rotating at high speed. A very small space or floating height between the magnetic head and the disk is created by the viscous air flow. Recording and retrieving of data is accomplished when the head is floating over the surface of the magnetic disk.
The recording density of the magnetic disk device is inversely proportional to the floating height of the magnetic head above the surface of the magnetic disk. It has been the tendency to decrease the floating height, and recently the floating height has reached the level of 50 nm. To comply with the requirement for a lower floating height, a sputtering disk has been used as the magnetic disk in a magnetic disk device.
A sputtering disk is formed by sputtering a magnetic material layer in forming the magnetic disk. The flatness of a magnetic disk is defined, for example, by its average surface roughness Ra. For a sputtering disk, an average surface roughness Ra of 20 to 5 nm has been achieved, making the sputtering disk advantageous in the objective of decreasing the floating height of the magnetic head.
Also, to comply with the requirements for a low floating height magnetic head, a negative pressure type magnetic head slider has been used wherein negative air pressure is introduced. Incoming air flow at the leading edge of the magnetic head slider is compressed, then released at a groove part to thereby generate the negative pressure (below atmospheric pressure condition). This creates a negative air pressure force that keeps the floating height constant between the inner circumference and outer circumference of the magnetic disk, despite the differences in surface linear speed therebetween.
As a result of recent advances in magnetic disk devices that are directed toward lowering the floating height of the magnetic head with respect to the magnetic disk, the following problems have occurred.
In a magnetic disk device, dust, fine oil mist and/or organic gases generated from the bearings and other lubricated, moving parts mix with the air inside the device. These contaminants float in the air within the device and until now have not caused any problem because the floating height between the magnetic head and the disk has not been so narrow as it is with recently developed magnetic disk devices. Now, since the floating height is significantly decreased, the contaminants generated from the bearings, among others, have the possibility of being lodged in the narrow space between the magnetic head and the magnetic disk causing magnetic head crash and damage to the magnetic head and the magnetic disk.
During the operation of the device, the contaminants floating in the air, especially the oil mist and the organic gases, adhere to the magnetic head slider. As a result, stiction between the head slider and the magnetic disk results. This can prevent rotation of the magnetic disk, which leads to the possibility of starting failure of the magnetic disk device due to the available starting torque. Also, there is a possibility that the magnetic disk can be damaged due to stiction caused by flaking off on the surface of the magnetic disk where the head slider adheres to the disk. This can be caused when a force larger than the normal starting torque is used to start rotation of the magnetic disk.
In magnetic disk devices of the prior art, it has been proposed that an electrostatic filter be used to collect floating contaminants in the air of a magnetic disk device. This proposal has been made in Japanese Application No. 5-62450. In another proposal, disclosed by Japanese Patent Application No. 6-36546, a filter is used in an air flow path arranged between a part near the rotating shaft of the carriage that drives the magnetic head and a part near the magnetic disk. The filter in the air flow path is intended to collect oil mist to prevent the oil mist from contaminating the air space within the device.
It has also been proposed in the prior art to provide a magnetic disk device having an enclosed air space with an outer circulating path. The air that flows through an inner part of the air space is passed through a filter to the outer circulation path to trap organic gases. Thereafter, the air in the outer circulation path that has been filtered is returned to the inner air space, or the interior of the device where the magnetic disk is present.